Removal of nitrogen oxides from coal-fired flue gas by gas-like phase chlorine dioxide

The flue gas emitted by coal-fired power plants contains a large amount of nitrogen oxides,which not only causes great harm to the ecological environment,but also is one of the main causes of smog. However,the main compo- nent of nitrogen oxides is NO,and the insoluble nature of NO makes it difficult to remove in a conventional desulfuriza- tion tower. In order to economically and effectively remove nitrogen oxides from coal-fired flue gas,the oxidative ab- sorption method was used for denitration research. By comparing the oxidation performance of different oxidants,ClO2 was selected as the oxidant,and it was gasified at 140 ℃ to be converted into a gas-phase-like oxidant. The NO in the flue gas was pre-oxidized into NO2 which is easily soluble in water,and then combined with the saturated calcium hy- droxide solution to absorb the oxidation product for the denitration of coal-fired flue gas. Electron paramagnetic reso- nance (ESR) and ·OH inhibitor addition experiments showed that the gas phase ClO2 generated strong oxidizing rad- icals such as ·OH during the oxidation process,which greatly promoted the oxidation of NO. The experimental results showed that the denitration efficiency increases with the increase of molar ratio ( ClO2 / NO). When the molar ratio (ClO2 / NO) was more than 0. 84,the removal efficiency increased slowly. In the range of 110 -170 ℃ ,the effect of temperature on NO removal was weak. The acidic condition was beneficial to the increase of NO removal,but the over- all effect was small. When SO2 and NO coexisted in the flue gas,the gas phase ClO2 preferentially oxidized NO in the flue gas. The optimum reaction conditions are:molar ratio (ClO2 / NO)= 0. 84,reaction temperature of 140 ℃ ,pH = 3, and the oxidative removal efficiency of NO can reach 92. 5% . The analysis of oxidation products by ion chromatogra- phy indicated that the main oxidation product of NO was NO- and proposed the mechanism of oxidative removal of NO in flue gas by gas-phase ClO2 . It indicated that the gas phase ClO2 combined with lye oxidation absorption has good in- dustrial application prospects.